U.S. patent application number 13/512521 was filed with the patent office on 2012-11-22 for method and arrangement for network nodes of a wireless communication network.
Invention is credited to Ylva Jading, Muhammad Kazmi, Bengt Lindoff.
Application Number | 20120294239 13/512521 |
Document ID | / |
Family ID | 42342713 |
Filed Date | 2012-11-22 |
United States Patent
Application |
20120294239 |
Kind Code |
A1 |
Lindoff; Bengt ; et
al. |
November 22, 2012 |
Method and Arrangement for Network Nodes of a Wireless
Communication Network
Abstract
A method of operating a wireless network node of a wireless
communication network is disclosed. The wireless network nodes have
at least first and second downlink transmission modes, the first
downlink transmission mode comprising normal operation of a
particular network node and being applicable when a number of
active terminals in a cell associated with the particular network
node is greater than a first mode threshold value, and the second
downlink transmission mode comprising restricted downlink
transmission of the particular network node and being applicable
when the number of active terminals in the cell associated with the
particular network node is less than or equal to a second mode
threshold value. The method comprises transmitting a signal
indicative of a current downlink transmission mode of the wireless
network node. Corresponding computer program product and
arrangement are also disclosed.
Inventors: |
Lindoff; Bengt; (Bjarred,
SE) ; Jading; Ylva; (Stockholm, SE) ; Kazmi;
Muhammad; (Bromma, SE) |
Family ID: |
42342713 |
Appl. No.: |
13/512521 |
Filed: |
November 30, 2010 |
PCT Filed: |
November 30, 2010 |
PCT NO: |
PCT/EP2010/068498 |
371 Date: |
August 5, 2012 |
Current U.S.
Class: |
370/328 |
Current CPC
Class: |
H04W 88/08 20130101;
Y02D 70/1262 20180101; Y02D 70/24 20180101; Y02D 30/70 20200801;
Y02D 70/25 20180101; H04W 52/0232 20130101; Y02D 70/1242
20180101 |
Class at
Publication: |
370/328 |
International
Class: |
H04W 4/00 20090101
H04W004/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2009 |
EP |
09180306.4 |
Claims
1. A method of operating a wireless network node of a wireless
communication network, wherein the wireless network node has at
least first and second downlink transmission modes, the first
downlink transmission mode comprising normal operation of the
network node and being applicable when a number of active terminals
in a cell associated with the network node is greater than a first
mode threshold value, the second downlink transmission mode
comprising restricted downlink transmission of the network node and
being applicable when the number of active terminals in the cell
associated with the network node is less than or equal to a second
mode threshold value, the restricted downlink transmission
comprising information that assists active terminals not served by
the cell in finding the cell and/or non-active terminals camping on
the cell to stay in synchronization with the wireless communication
network, the method comprising: transmitting a signal indicative of
a current downlink transmission mode of the wireless network
node.
2. The method of claim 1, wherein the signal indicative of the
current downlink transmission mode comprises an identification of
the current downlink transmission mode.
3. The method of claim 1, wherein the signal indicative of the
current downlink transmission mode comprises an indication of a
change of the current downlink transmission mode.
4. The method of claim 3 comprising, when the current downlink
transmission mode is the first downlink transmission mode:
determining if the network node should change the current downlink
transmission mode to the second downlink transmission mode; and if
it is determined that the network node should change the current
downlink transmission mode to the second downlink transmission
mode: transmitting the signal comprising the indication of the
change of the current downlink transmission mode; and changing the
current downlink transmission mode to the second downlink
transmission mode.
5. The method of claim 4, wherein the step of determining if the
network node should change the current downlink transmission mode
to the second downlink transmission mode comprises: evaluating the
number of active terminals served by the cell; and determining that
the network node should change the current downlink transmission
mode to the second downlink transmission mode if the number of
active terminals served by the cell is less than or equal to the
second mode threshold value.
6. The method of claim 4, wherein the step of determining if the
network node should change the current downlink transmission mode
to the second downlink transmission mode comprises: evaluating the
number of active terminals served by the cell; determining that the
network node should change the current downlink transmission mode
to the second downlink transmission mode if the number of active
terminals served by the cell is less than or equal to a first mode
transition threshold value, wherein the first mode transition
threshold value is larger than the second mode threshold value; and
forcing handover of a particular number of the active terminals
served by the cell to other cells prior to the step of changing the
current downlink transmission mode to the second downlink
transmission mode, wherein the particular number is larger than or
equals the number of active terminals minus the second mode
threshold value.
7. The method of claim 3 comprising, when the current downlink
transmission mode is the second downlink transmission mode:
determining if the network node should change the current downlink
transmission mode to the first downlink transmission mode; and if
it is determined that the network node should change the current
downlink transmission mode to the first downlink transmission mode:
changing the current downlink transmission mode to the first
downlink transmission mode; and transmitting the signal comprising
the indication of the change of the current downlink transmission
mode.
8. The method of claim 7, wherein the step of determining if the
network node should change the current downlink transmission mode
to the first downlink transmission mode comprises: evaluating a
number of terminals that will become active and that could be
served by the cell and the number of active terminals served by the
cell; and determining that the network node should change the
current downlink transmission mode to the first downlink
transmission mode if the number of terminals that will become
active and that could be served by the cell plus the number of
active terminals served by the cell is greater than a second mode
transition threshold value.
9. The method of claim 1, further comprising: transmitting a signal
indicative of a current downlink transmission mode of a
neighbouring network node of the wireless network node.
10. The method of claim 9, further comprising: determining a change
of the current downlink transmission mode of the neighbouring
network node; and wherein the step of transmitting the signal
indicative of the current downlink transmission mode of the
neighbouring network node comprises transmitting an indication of
the change of the current downlink transmission mode of the
neighbouring network node.
11. The method of claim 1, wherein the signal indicative of the
current downlink transmission mode of the wireless network node is
transmitted using at least one of: a broadcast channel; a paging
channel; a synchronization channel; a shared channel; a dedicated
channel; a physical control channel; and a message dedicated for
transmission of the signal.
12. The method of claim 1, wherein at least one of the first and
second mode threshold values equals zero.
13. A computer program product comprising a computer readable
medium, having thereon a computer program comprising program
instructions, the computer program being loadable into a
data-processing unit of a wireless network node of a wireless
communication network, wherein the wireless network node has at
least first and second downlink transmission modes, the first
downlink transmission mode comprising normal operation of the
network node and being applicable when a number of active terminals
in a cell associated with the network node is greater than a first
mode threshold value, the second downlink transmission mode
comprising restricted downlink transmission of the network node and
being applicable when the number of active terminals in the cell
associated with the network node is less than or equal to a second
mode threshold value, the restricted downlink transmission
comprising information that assists active terminals not served by
the cell in finding the cell and/or non-active terminals camping on
the cell to stay in synchronization with the wireless communication
network, the computer program being adapted to cause the
data-processing unit to execute at least the following step when
the computer program is run by the data-processing unit:
determining if the network node should change a current downlink
transmission mode; and if it is determined that the network node
should change the current downlink transmission mode: transmitting
a signal comprising an indication of the change of the current
downlink transmission mode; and changing the current downlink
transmission mode.
14. An arrangement for a wireless network node of a wireless
communication network, wherein the wireless network node has at
least first and second downlink transmission modes, the first
downlink transmission mode comprising normal operation of the
network node and being applicable when a number of active terminals
in a cell associated with the network node is greater than a first
mode threshold value, the second downlink transmission mode
comprising restricted downlink transmission of the network node and
being applicable when the number of active terminals in the cell
associated with the network node is less than or equal to a second
mode threshold value, the restricted downlink transmission
comprising information that assists active terminals not served by
the cell in finding the cell and/or non-active terminals camping on
the cell to stay in synchronization with the wireless communication
network, comprising: circuitry arranged to determine if the network
node should change a current downlink transmission mode; a
controller arranged to change the current downlink transmission
mode if it is determined that the network node should change the
current downlink transmission mode; and a transmitter arranged to
transmit a signal comprising an indication of the change of the
current downlink transmission mode.
15. A wireless network node comprising the arrangement according to
claim 14.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to the field of
operating network nodes in a wireless communication network where
the network nodes have two operation modes, such as a high activity
mode and a low activity mode.
BACKGROUND
[0002] Energy consumption has always been and still is an important
issue for mobile terminals of wireless communication systems such
as cellular systems. Recently, trends in environmental friendly
technology make it important to reduce the energy consumption also
for the network nodes (e.g. base stations--BS, NodeB, eNodeB, etc).
Unlike terminals, which have possibilities to go into idle (or
sleep) mode once they are not active, a network node needs to
always transmit some signals (e.g. pilots, synchronization symbols
and broadcast messages) so that camping terminals may stay in
synchronization (in sync) with the network.
[0003] In an example scenario, when a network node serves a cell
with many active terminals and some idle terminals, the network
node may need to continuously transmit pilots, synchronization
signals, etc, in order to maintain connection to the terminals.
However, in an alternative scenario, when a network node serves a
cell where all terminals are in an idle state (or in an active
state with very low activity), the situation is somewhat different.
In such scenarios, the terminals do not receive any data (or only a
very small amount of data). The terminals only need to do mobility
measurements (such as measurements for cell reselection or
handover) and listen to paging messages. In such scenarios, a
network node which is transmitting according to its conventional
transmission scheme will waste a lot of energy.
[0004] Proposals considering an ability to put network nodes with a
low load (e.g. serving no or few active terminals) into an "idle"
state have been discussed.
[0005] An "idle" state (or energy saving mode) of a network node
may be applicable when there are no active terminals in a cell
associated with the network node. Alternatively or additionally,
the "idle" state of a network node may be applicable when the
number of active terminals in the cell are less than or equal to a
threshold.
[0006] In the same manner a normal operation mode of a network node
may be applicable when there is at least one active terminal in a
cell associated with the network node. Alternatively or
additionally, the normal operation mode may be applicable when the
number of active terminals in the cell is greater than a threshold
(which may or may not be the same as the threshold for the "idle"
state).
[0007] Generally, the "idle" state may comprise restricted downlink
transmissions. For example, some signals may be transmitted
intermittently instead of continuously, and/or some signals may be
transmitted using only part of the cell transmission bandwidth,
and/or some signals may not be transmitted at all.
[0008] An example of a network node "idle" state may be a low
activity mode of the network node comprising restricted or reduced
downlink transmissions. One possible approach might be to reduce
the amount of transmitted signals or channels to an absolute
minimum. There are numerous possible ways to achieve a low activity
mode of a network node, and the possibilities may vary depending on
the access technology under consideration. Definitions and
particulars of a network node "idle" state may be specified in
standardization documentation for the applicable standards. Low
activity state, low transmission state, restricted state, and
restricted transmission state are other examples of possible
terminologies that may be used for the idle state. The skilled
person recognizes that all of these terms may have similar or the
same meaning. Hereinafter, the terms idle state, energy saving mode
and low activity mode will be used. A few examples of approaches
that are applicable to UMTS LTE (Universal Mobile Telecommunication
Standard Long Term Evolution, Release 9, 10 and onwards;
E-UTRAN--Evolved UMTS Terrestrial Radio Access Network) are given
in the following. It should be noted however, that these are merely
examples and by no way limiting to the invention.
[0009] In UMTS LTE it may be sufficient for a NodeB in the "idle"
state to transmit only synchronization signals (PSS--Primary
Synchronization Sequence/SSS--Secondary Synchronization Sequence)
and physical broadcast information (P-BCH--Physical Broadcast
CHannel) together with pilot symbols (also denoted reference
signals and used for e.g. channel estimation) in association with
the P-BCH transmission. These signals are transmitted in well
defined OFDM symbols in sub-frames 0 and 5 in both FDD (Frequency
Division Duplex) and TDD (Time Division Duplex). If such an
approach is used, the NodeB can reduce its duty cycle significantly
and basically transmit information only in a few OFDM symbols of
the sub-frames 0 and 5.
[0010] If more limited pilot (or reference) signals are transmitted
in the energy saving mode (e.g. only in sub-frames 0 and 5, and
only over 6 central resource blocks, then a terminal may perform
measurements over a smaller bandwidth than when the network node is
in non-energy saving mode.
[0011] In another approach that further reduces the amount of
transmissions in UMTS LTE, only the synchronization signals
(PSS/SSS) are transmitted by the network node when it is in the
"idle" state. As in the previous example above these signals are
transmitted in sub-frames 0 and 5. The transmission takes place
over 6 central resource blocks regardless of the actual cell
transmission bandwidth (i.e. the bandwidth in the active
state).
[0012] A problem that arises when reducing the number of pilots is
that the terminal needs to rely on fewer symbols for keeping in
sync with the network node.
[0013] Another problem that arises is that the operations of a
terminal (e.g. measurements, paging listening, etc) designed to
work well when the corresponding network node is in a normal
operation mode may not be optimal when the corresponding network
node is in the "idle" state.
[0014] Thus, there is a need for methods and arrangements for
enabling a terminal to operate adequately in a wireless
communication network having network nodes with two operational
modes, e.g. a high activity mode (conventional operation) and a low
activity mode ("idle" state).
SUMMARY
[0015] It should be emphasized that the term "comprises/comprising"
when used in this specification is taken to specify the presence of
stated features, integers, steps, or components, but does not
preclude the presence or addition of one or more other features,
integers, steps, components, or groups thereof.
[0016] It is an object of the invention to obviate at least some of
the above disadvantages and to provide methods and arrangements for
enabling a terminal to operate adequately in a wireless
communication network having network nodes with two operational
modes.
[0017] The two operational modes may be operable to set the entire
network node operation into a high activity operational mode or a
low activity operational mode. It should be noted, however, that
the two operational modes may alternatively or additionally be
applicable on cell level (in the case when a network node serves
several cells) and/or on carrier level (in the case when a network
node or cell applies more than one carriers). Thus, to give an
example, the same network node may simultaneously serve one of its
cells in a low activity mode and another one of its cells in high
activity mode.
[0018] According to a first aspect of the invention, this is
achieved by a method of operating a wireless network node of a
wireless communication network. The wireless network node has at
least first and second downlink transmission modes. The first
downlink transmission mode comprises normal operation of the
network node and is applicable when a number of active terminals in
a cell associated with the network node is greater than a first
mode threshold value. The second downlink transmission mode
comprises restricted downlink transmission of the network node and
is applicable when the number of active terminals in the cell
associated with the network node is less than or equal to a second
mode threshold value. The restricted downlink transmission
comprises information that assists active terminals not served by
the cell in finding the cell and/or non-active terminals camping on
the cell to stay in synchronization with the wireless communication
network. The method comprises transmitting a signal indicative of a
current downlink transmission mode of the wireless network
node.
[0019] In some embodiments, the signal indicative of the current
downlink transmission mode may comprise an identification of the
current downlink transmission mode. In some embodiments, the signal
indicative of the current downlink transmission mode may comprise
an indication of a change of the current downlink transmission
mode.
[0020] In some embodiments, the method may comprise determining if
the network node should change a current downlink transmission
mode. If it is determined that the network node should change the
current downlink transmission mode the method may further comprise
transmitting a signal comprising an indication of the change of the
current downlink transmission mode and changing the current
downlink transmission mode.
[0021] The method may, in some embodiments, comprise determining if
the network node should change the current downlink transmission
mode to the second downlink transmission mode when the current
downlink transmission mode is the first downlink transmission mode.
If it is determined that the network node should change the current
downlink transmission mode to the second downlink transmission mode
the method may further comprise transmitting the signal comprising
the indication of the change of the current downlink transmission
mode and changing the current downlink transmission mode to the
second downlink transmission mode.
[0022] In some embodiments, the step of determining if the network
node should change the current downlink transmission mode to the
second downlink transmission mode may comprise evaluating the
number of active terminals served by the cell and determining that
the network node should change the current downlink transmission
mode to the second downlink transmission mode if the number of
active terminals served by the cell is less than or equal to the
second mode threshold value.
[0023] In some embodiments, the step of determining if the network
node should change the current downlink transmission mode to the
second downlink transmission mode may comprises evaluating the
number of active terminals served by the cell and determining that
the network node should change the current downlink transmission
mode to the second downlink transmission mode if the number of
active terminals served by the cell is less than or equal to a
first mode transition threshold value, wherein the first mode
transition threshold value is larger than the second mode threshold
value.
[0024] The method may also comprise forcing handover of a
particular number of the active terminals served by the cell to
other cells prior to the step of changing the current downlink
transmission mode to the second downlink transmission mode, wherein
the particular number is larger than or equals the number of active
terminals minus the second mode threshold value.
[0025] The method may, in some embodiments, comprise determining if
the network node should change the current downlink transmission
mode to the first downlink transmission mode when the current
downlink transmission mode is the second downlink transmission
mode. If it is determined that the network node should change the
current downlink transmission mode to the first downlink
transmission mode the method may further comprise changing the
current downlink transmission mode to the first downlink
transmission mode and transmitting the signal comprising the
indication of the change of the current downlink transmission
mode.
[0026] In some embodiments, the step of determining if the network
node should change the current downlink transmission mode to the
first downlink transmission mode may comprise evaluating a number
of terminals that will become active and that could be served by
the cell and the number of active terminals served by the cell, and
determining that the network node should change the current
downlink transmission mode to the first downlink transmission mode
if the number of terminals that will become active and that could
be served by the cell plus the number of active terminals served by
the cell is greater than a second mode transition threshold value.
The method may further comprise transmitting a signal indicative of
a current downlink transmission mode of a neighbouring network node
of the wireless network node according to some embodiments of the
invention.
[0027] In such embodiments, the method may further comprise
determining a change of the current downlink transmission mode of
the neighbouring network node and the step of transmitting the
signal indicative of the current downlink transmission mode of the
neighbouring network node may comprise transmitting an indication
of the change of the current downlink transmission mode of the
neighbouring network node.
[0028] In some embodiments, the signal indicative of the current
downlink transmission mode of a particular network node may further
comprise additional information. The additional information may
comprise at least one of: [0029] information regarding when a
change in the downlink transmission mode occurs, [0030] information
regarding a duration of time in which the particular network node
will maintain a new downlink transmission mode [0031] information
regarding an identity (e.g. a physical cell identity or a cell
global identity) of the particular network node, [0032] information
regarding a carrier frequency of the particular network node,
[0033] information regarding a radio access technology of the
particular network node, [0034] information regarding transmission
parameters of the second downlink transmission mode (e.g.
transmission bandwidth of pilot signals), [0035] information
regarding which signals (if any) are transmitted during the second
downlink transmission mode, [0036] information regarding one or
more component carriers of the particular network node in a
multi-carrier or carrier aggregation system.
[0037] In some embodiments, the signal indicative of the current
downlink transmission mode of the wireless network node may be
transmitted using at least one of: a broadcast channel, a paging
channel, a synchronization channel, a shared channel, a dedicated
channel, a physical control channel, and a message dedicated for
transmission of the signal.
[0038] In some embodiments, the second operation mode may comprise
intermittent downlink transmission of the particular network
node.
[0039] The first and/or second mode threshold value may equal zero
according to some embodiments.
[0040] A second aspect of the invention is a computer program
product comprising a computer readable medium, having thereon a
computer program comprising program instructions, the computer
program being loadable into a data-processing unit and adapted to
cause the data-processing unit to execute method steps according to
the first aspect of the invention when the computer program is run
by the data-processing unit.
[0041] A third aspect of the invention is an arrangement for a
wireless network node of a wireless communication network, wherein
the wireless network node has at least first and second downlink
transmission modes. The first downlink transmission mode comprises
normal operation of the network node and is applicable when a
number of active terminals in a cell associated with the network
node is greater than a first mode threshold value. The second
downlink transmission mode comprises restricted downlink
transmission of the network node and is applicable when the number
of active terminals in the cell associated with the network node is
less than or equal to a second mode threshold value. The restricted
downlink transmission comprises information that assists active
terminals not served by the cell in finding the cell and/or
non-active terminals camping on the cell to stay in synchronization
with the wireless communication network. The arrangement comprises
circuitry arranged to determine if the network node should change a
current downlink transmission mode, a controller arranged to change
the current downlink transmission mode if it is determined that the
network node should change the current downlink transmission mode,
and a transmitter arranged to transmit a signal comprising an
indication of the change of the current downlink transmission
mode.
[0042] A fourth aspect of the invention is a wireless network node
comprising the arrangement according the third aspect of the
invention.
[0043] In some embodiments, the second, third and fourth aspects of
the invention may additionally have features identical with or
corresponding to any of the various features as explained above for
the first aspect of the invention.
[0044] An advantage of some embodiments of the invention is that
the terminal is informed of the current operational mode of the
network node. The terminal may adapt its operations accordingly.
For example, the terminal may adapt one or more of its
time/frequency synchronization, its channel estimation algorithms,
and its measurement algorithms relating to cell reselection,
handover and/or radio link monitoring based on the current
operational mode of the network node.
[0045] Another advantage of some embodiments of the invention is
that the terminal behavior (in terms of robustness, performance
and/or power consumption) may be improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] Further objects, features and advantages of the invention
will appear from the following detailed description of embodiments
of the invention, with reference being made to the accompanying
drawings, in which:
[0047] FIG. 1 is a schematic drawing illustrating a plurality of
mobile terminals and a base station site which may comprise an
arrangement according to some embodiments of the invention;
[0048] FIG. 2 is a flowchart illustrating example method steps
according to some embodiments of the invention;
[0049] FIG. 3 is a flowchart illustrating example method steps
according to some embodiments of the invention;
[0050] FIG. 4 is a schematic diagram illustrating a computer
program product according to some embodiments of the invention;
and
[0051] FIG. 5 is a block diagram illustrating an example
arrangement according to some embodiments of the invention.
DETAILED DESCRIPTION
[0052] In the following, embodiments of the invention will be
described where a network node of a wireless network transmits an
indication of its current operational mode to one or more terminals
of the wireless network.
[0053] The description of embodiments of the invention will focus
on UMTS LTE: However, it is to be understood that the invention is
not limited to application is such systems. Furthermore, the term
NodeB is used in the description, but this is in no way to be
construed as limiting. Contrarily, embodiments of the invention are
equally applicable in the context of any type of network node, such
as any base station (eNodeB, femto cell, home base station, home
eNodeB, home NodeB) or any radio network node having base station
functionalities and capabilities.
[0054] First, a general description of example network signaling
and some example tasks that may need to be performed by a terminal
(or is desirable that a terminal performs) in a wireless
communication network is given.
[0055] In order for a terminal to detect a cell and keep itself in
synchronization with the network, a number of physical signals
typically need to be transmitted by the network. In general, the
terminal needs some type of synchronization signal(s) to
synchronize itself with the system (e.g. P-SCH (Primary
Synchronization CHannel) termed PSS (Primary Synchronization
Sequence) and S-SCH (Secondary Synchronization CHannel) termed SSS
(Secondary Synchronization Sequence) in UMTS and UMTS LTE).
[0056] Furthermore, some kind of reference symbols or pilot signals
are typically required (e.g. CPICH (Common PIlot CHannel) in UMTS
and RS (Reference Symbols) in UMTS LTE). These signals may be used
to measure the signal strength and/or signal quality of a cell.
They may also be used to estimate the radio channel used for data
demodulation. In UMTS LTE FDD, RS typically used for measurements
are transmitted in sub-frames 0, 4, 5, 9, from antenna port 0, and
in the central 6 resource blocks.
[0057] The cell might also need to transmit broadcast information
in order for a terminal to know various parameters (e.g. needed for
setting up a connection). Depending on the cellular system, such
information is transmitted on different physical channels. In UMTS
LTE, broadcast information is sent via the physical broadcast
channel (PBCH) and the physical downlink shared channel (PDSCH).
The PBCH is transmitted in sub-frame 0 and contains the master
information block (MIB), which carries important information such
as cell bandwidth, one or more antenna ports, system frame number
(SFN), etc. Other, more detailed, information may be transmitted
via one or more of several system information blocks (SIB), which
are mapped on PDSCH and transmitted in sub-frame 5 in UMTS LTE. In
UMTS, there is only one broadcast channel, which contains both MIB
and SIBs.
[0058] Thus, in UMTS LTE, the PSS/SSS and the broadcast channel
(BCH) are used for the above purposes. It is noted, however, that
some carriers may carry PSS/SSS but no BCH. It is also noted that
other systems may employ other setups.
[0059] Information like the one described above (synchronization
signals, reference signal, broadcast information) are commonly
denoted Necessary Cell Identity Information (NCII), and is an
example of information that may be transmitted by a network node in
energy saving mode.
[0060] One example task to be performed by a terminal is performing
mobility measurements. Depending on the current mode of the
terminal, the terminal may perform any of two types of mobility,
namely idle mode mobility (e.g. for cell reselection purposes) or
connected mode mobility (e.g. for handover purposes). In most
applications, the cell reselection is a mainly terminal autonomous
function without any direct intervention of the network. However,
the terminal behaviour in this mobility scenario could--to some
extent--be controlled by broadcasted system parameters and by
performance specification. The handover, on the other hand, is in
general fully controlled by the network through explicit terminal
specific commands and by performance specification.
[0061] For both idle mode and connected mode, mobility decisions
may mainly be based on downlink neighbor cell measurements (which
may be of the same or different type for the two terminal
operational modes).
[0062] For example, in UMTS LTE (E-UTRAN--Evolves UMTS Terrestrial
Radio Access Network) the following downlink neighbor cell
measurements (measured for serving and neighboring cells) are
specified primarily for mobility purpose (see the specification
document 3GPP TS 36.214, "Evolved Universal Terrestrial Radio
Access (E UTRA); Physical layer measurements"): [0063] Reference
symbol received power (RSRP), which is signal strength measurement,
and [0064] Reference symbol received quality (RSRQ), which is
signal quality measurement (RSRQ=RSRP/carrier RSSI (Received Signal
Strength Indication)).
[0065] Another example task for the terminal concerns radio link
monitoring. In general, the radio link monitoring (RLM) procedure
enables the terminal to detect whether it is out of sync or in sync
with the serving cell.
[0066] The procedure may be used when the terminal is in RRC (Radio
Resource Control) connected mode. In UMTS LTE, the RLM procedure
and the corresponding requirements are specified in the
specification documents 3GPP TS 36.331, "Evolved Universal
Terrestrial Radio Access (E UTRA); Radio Resource Control (RRC);
Protocol specification" and 3GPP TS 36.133, "Evolved Universal
Terrestrial Radio Access (E UTRA); Requirements for support of
radio resource management".
[0067] In some applications of UMTS LTE, the terminal measures the
serving cell downlink quality based on a common reference signal to
determine whether it is out of sync or in sync with the serving
cell. After N successive out of sync determinations have been
registered (where N is a network configured parameter), a radio
link failure (RLF) procedure may be initiated. Upon completion of
the RLF procedure, the terminal typically turns off its transmitter
and may attempt to establish (or re-establish) a connection to the
most suitable cell (e.g. the cell with the strongest measured
signal).
[0068] When a terminal is located in a wireless communication
system where at least one network node may be in one of two
operational modes as described above, it may be an advantage for
the terminal to know the current operational mode of the network
node (for example to be able to perform any of the above example
tasks as accurately and resource efficiently as possible).
[0069] Thus, there is a need for methods and arrangements for
enabling a terminal to operate adequately in a wireless
communication network having network nodes with two operational
modes. To be able to achieve this, it is beneficial for the
terminal to have knowledge of the current operational mode of
network nodes in the network.
[0070] One way of achieving this is to transmit information from
the network to the terminal indicating a current operational mode
of one or more network nodes.
[0071] The gained knowledge regarding the current operational mode
of the network node may be used to adapt further operations of the
terminal. For example, if the current operational mode of the
network node is an energy saving mode ("idle" state) the terminal
may use synchronization signals (e.g. PSS/SSS) for one or more of:
RLM, mobility measurements (e.g. signal strength/quality
measurements for handover and/or cell re-selection), positioning
related measurements (e.g. time difference of arrival of signals
from different cells), time tracking, frequency tracking (e.g.
automatic frequency control (AFC)), mobile speed detection, and
Doppler estimation. On the other hand, if the current operational
mode of the network node is a normal operation mode ("active"
state) the terminal may use reference symbols (e.g. pilot symbols)
for one or more of these purposes. In some embodiments, the gained
knowledge may be used to adapt a time pattern based on the current
downlink transmission mode, wherein the time pattern specifies when
a receiver of the terminal is turned on (e.g. in discontinuous
reception, DTX, mode of the terminal).
[0072] The transmitted information may comprise either or both of a
direct indication of the current operational mode and an indication
of a change of operational mode. Either of these types information
may be conveyed using a single information bit.
[0073] The information may be transmitted to terminals connected to
or camping on a cell associated with the network node under
consideration. In some embodiments, information regarding the mode
or change of mode of neighboring cells may also be transmitted. The
terminal may adapt its operation based on the mode of a network
node (serving/camping or neighboring). This adaptation may improve
the terminal behavior (e.g. in terms of robustness, performance
and/or power consumption) as exemplified above.
[0074] Transmission of the information may, for example, be
accomplished via broadcasting the information (e.g. on BCH),
sending it via a synchronization channel (e.g. PSS/SSS in UMTS
LTE), including it in paging messages to the terminals, sending a
message dedicated for this purpose, including the information in
transmissions on a dedicated or terminal specific channel (e.g.
PDCCH or PDSCH in UMTS LTE), including the information in
transmissions on a SIB, or using any other means of conveying the
information.
[0075] According to some embodiments, additional information may
also be included in such transmissions. For example, information
regarding a time instant when a mode change will occur, a duration
of the mode (e.g. during which time the network node will stay in
an energy saving mode), and/or the setup of the restricted
transmission in an energy saving mode (e.g. transmission parameters
and/or which signals will be transmitted and when) may be
included.
[0076] An example of a transmission parameter that may be included
in the additional information is the bandwidth used to transmit a
restricted or reduced number of pilot signals or reference signals
(RS). In LTE, for example, the reference signals are in general
transmitted over the entire bandwidth. However, in low activity
mode the reference signals could be transmitted over fewer resource
blocks (e.g. over the 6 central resource blocks). Hence, in this
example, the base station may signal to the terminal (e.g. before
its transfer to low activity mode) that the reference signal
transmission bandwidth in low activity mode will be 6 resource
blocks.
[0077] Other examples of additional information include information
regarding an identity, radio access technology, and/or carrier
frequency of the network node associated with the signaled mode
(particularly relevant when the mode of neighboring nodes is
signaled as will be explained in the following).
[0078] Another specific example of additional information that may
be required or desirable relates to a multi-carrier system, where
the same terminal is served over more than one carrier frequency in
the downlink and/or in the uplink to enhance the data rate. A
multi-carrier system (also referred to as carrier aggregation) is
part of the evolution of UMTS LTE and UMTS (WCDMA and UTRAN TDD).
For instance, in an UMTS LTE multi-carrier system, the network may
serve (i.e. transmit data) over multiple 20 MHz carriers (e.g. 4
component carriers each of 20 MHz). For the purpose of energy
saving one or more component carriers may be partially or fully
turned off in a low activity operational mode. Hence, in such an
example, the additional information may include information
regarding which one or more of the component carriers in the
serving (and/or neighbor) cells will be used also in a low activity
operational mode and/or which of the component carriers are used in
a high activity operational mode.
[0079] In general, a synchronization channel is always present in
most systems, so this is a convenient and robust channel for
conveying network mode information. In order to reduce overhead it
is preferred in some embodiments to not reserve more than one or
two bits on the synchronization channel for carrying of the mode
information. In such embodiments, it is therefore not feasible to
provide more detailed additional information.
[0080] According to some embodiments, there may be several
definitions of the "idle" state of a network node specified. For
example, there may be several ways of organizing transmitted
signals/channels to save energy. In such embodiments, a terminal
may be informed of the current "idle" state type using methods
similar to those described above.
[0081] FIG. 1 illustrates a plurality of mobile terminals 102, 103,
104, 105, 106. The mobile terminals are adapted to connect to a
mobile telecommunication network via a wireless link to a radio
base station 101 of a base station site 100. The base station 101
may, for example, comprise an arrangement as will be described in
connection to FIG. 5 and/or perform any of the methods as described
in connection to FIGS. 2 and 3.
[0082] FIG. 2 illustrates an example method 200 that may be
performed by a network node (e.g. a base station) according to some
embodiments of the invention.
[0083] When the network node is in a normal operation mode (step
210), it may evaluate whether or not it should change operational
mode to an energy saving mode. Such an evaluation may be performed
on regular basis (e.g. at regular time intervals and/or at specific
times, on specific days, etc.) or based on some related conditions
(e.g. each time a connection to a terminal is terminated).
[0084] If it is determined that the network node should not change
operational mode (NO-path out of step 220) the network node stays
in the current mode (step 210). An indication to this end may be
transmitted to terminals associated with the network node (optional
step 225).
[0085] If it is determined that the network node should change
operational mode (YES-path out of step 220) the process proceeds to
step 230, where an indication regarding the change is transmitted
to terminals associated with the network node. Additional
information may also be included in the transmission. The time
instant of the change may be signaled or may be pre-defined (e.g.
in a standardization document and for example as a particular
number of sub-frames or frames after sending the mode change
indication). Information regarding the time duration of the energy
saving mode may also be signaled if it is known to the system. In
some embodiments, a default duration of the energy saving mode may
be pre-defined (e.g. in a standardization document). Furthermore,
the NCII may also be transmitted from in step 230 according to some
embodiments of the invention. Then the network node changes mode to
an energy saving mode in step 240.
[0086] The determination in step 220 of whether or not to change
mode may be performed by comparing the number of active/connected
terminals associated by the network node (e.g. served by a cell of
the network node and/or requesting handover to the network node
and/or indicated by a neighboring node as being servable by the
network node under consideration) to a threshold (t1) as
illustrated in sub-step 221. Terminals that are about to become
active (e.g. terminals requesting access) may also be included in
the evaluation. The number of terminals to evaluate may be tracked
by a load indicator. The threshold may, for example, be set to zero
or any adequate positive value. If the number of terminals is
larger than the threshold (NO-path out of sub-step 221) it may be
determined that there should not be any change of mode (sub-step
222). If the number active of terminals less than or equal to the
threshold (YES-path out of sub-step 221) it may be determined that
there should be a change of mode (sub-step 223).
[0087] The transmission of the indication of the mode change of
step 230 may be combined with a forced handover of some or all of
the active terminals to neighboring network nodes before the actual
mode change takes place. This is illustrated by sub-step 231 and
optional sub-step 232. The need for performing sub-step 232 may
depend on the value of the threshold (t1), the number of terminals
that it is possible to serve for a network node in energy saving
mode and/or the number of terminals in the evaluation of step 220.
For example, if there where no active terminals in the evaluation
of step 220, there is no need to perform sub-step 232. Similarly,
if the threshold (t1) is set to zero, there is never any need to
perform sub-step 232. Yet similarly, if the number of active
terminals in the evaluation of step 220 may all be served by the
network node in its energy saving mode, there is no need to perform
sub-step 232. More generally, at it is preferable to force handover
of at least a number of terminals that equals the number of active
terminals minus the number of terminals that can be served in an
energy saving mode.
[0088] When the network node is in an energy saving operation mode
(step 250), it may evaluate whether or not it should change
operational mode to a normal operation mode. Such an evaluation may
be performed on regular basis (e.g. at regular time intervals
and/or at specific times, on specific days, etc.) or based on some
related conditions (e.g. each time a connection is requested by a
terminal).
[0089] If it is determined that the network node should not change
operational mode (NO-path out of step 260) the network node stays
in the current mode (step 250). An indication to this end may be
transmitted to terminals associated with the network node (optional
step 265).
[0090] If it is determined that the network node should change
operational mode (YES-path out of step 260) the process proceeds to
step 270, where the network node changes mode to a normal operation
mode. Then, an indication regarding the change is transmitted to
terminals associated with the network node in step 280. Additional
information may also be included in the transmission. The time
instant of the change may be signaled or may be pre-defined
similarly to what was described in relation to step 230.
Information regarding the time duration of the normal operation
mode may also be signaled if it is known to the system. In some
embodiments, a default duration of the normal operation mode may be
pre-defined (e.g. in a standardization document).
[0091] The determination in step 260 of whether or not to change
mode may be performed by comparing the number of active/connected
terminals associated by the network node (e.g. served by a cell of
the network node and/or requesting handover to the network node
and/or indicated by a neighboring node as being servable by the
network node under consideration) to a threshold (t2) as
illustrated in sub-step 261. The threshold t2 may or may not have
the same value as the threshold t1 of sub-step 221. Terminals that
are about to become active (e.g. terminals requesting access) may
also be included in the evaluation. The threshold may, for example,
be set to zero or any adequate positive value. If the number of
terminals is larger than the threshold (YES-path out of sub-step
261) it may be determined that there should be a change of mode
(sub-step 263). If the number active of terminals less than or
equal to the threshold (NO-path out of sub-step 261) it may be
determined that there should not be any change of mode (sub-step
262).
[0092] It is to be noted that the entire method 200 may be
performed by a single network node (e.g. a base station) or by a
combination of network nodes (e.g. steps 220 and 260 may be
performed by a base station controller or other network controller,
while the other steps may be performed by a base station).
[0093] It is to be noted that the thresholds t1 and t2 may relate
to the thresholds where the different modes are applicable (see
Background section). For example, if the normal operation mode is
applicable for situations when there are more than t3 active
terminals in a cell and the energy saving mode is applicable for
situations when there are less than or equal to t4 active terminals
in a cell, then the different thresholds may, in some embodiments,
be related according to any of the following examples: [0094]
t1<=t4 (if no handover is applicable, step 232), [0095] t1>t4
(if handover is applicable, step 232), [0096] t3=t4 [0097] t3<t4
[0098] t2>t3 (particularly helpful if t3 is equal to or close to
t4 and frequent mode changes should be avoided) [0099] t2=t3.
[0100] FIG. 3 illustrates an example method 300 that may be
performed by a network node (e.g. a base station) according to some
embodiments of the invention. In step 310, a network node acquires
information regarding the current status of a neighboring cell (or
network node). The information may concern an actual current mode
of the neighboring node and/or a change of mode. This information
may be acquired via reception of indications form the neighboring
node or via measurements performed by the network node under
consideration. In step 320, an indication regarding the mode of the
neighboring node is transmitted to terminals associated with the
network node under consideration.
[0101] The transmission of information of step 320 may be very
similar to the transmission of information in steps 225, 230, 231,
265 and/or 280 of FIG. 2 and is hence not described in great
detail. A difference, though, is that information regarding the
cell identity (e.g. PCI--physical cell identity--in UMTS and UMTS
LTE) of the neighboring node is typically transmitted along with
the indication in step 320. Other type of information transmitted
along with the indication in step 320 may comprise information
regarding a restricted transmission bandwidth in the situation
where only a part of the generally used bandwidth is to be used
during the energy saving mode. Another similar parameter that may
be transmitted along with the indication in step 320 is information
regarding a restricted transmission bandwidth of reference
signals.
[0102] Signaling of other parameters, such as carrier frequency
and/or radio access technology (RAT) of the neighboring node, may
also be useful.
[0103] For example if the serving cell operates according to UMTS
LTE and a neighboring cell that operates according to UMTS (WCDMA
or UTRAN TDD) will go into an energy saving mode or revert to the
normal operation from an energy saving mode, information regarding
the radio access technology of the neighboring node may be provided
to the terminal by the serving UMTS LTE cell. Such information may
comprise, but is by no means limited to, the target RAT identity,
the carrier frequency of the cell(s), cell identity (at least the
PCI). The information may also comprise other parameters as
mentioned above, such as timing information (e.g. starting time and
duration of the energy saving mode, or time for revert to normal
operational mode).
[0104] Another example includes a UMTS LTE FDD serving cell and one
or more target UMTS LTE TDD cells. In such an example, if one or
more of the UMTS LTE TDD cells prepare to transfer to energy saving
mode, the serving UMTS LTE FDD cell may signal information related
to those UMTS LTE TDD cells preparing for energy saving mode. If
one or more of the UMTS LTE TDD cells prepare to transfer to normal
operation mode, the serving UMTS LTE FDD cell may signal
information related to those UMTS LTE TDD cells.
[0105] Obviously, the methods 200 and 300 of FIGS. 2 and 3
respectively may be combined, and the method 300 may be performed
in parallel with the method 200 regardless if the network node
under consideration is in its normal operation mode or in an energy
saving mode.
[0106] FIG. 4 is a schematic drawing illustrating a computer
readable medium in the form of a CD-ROM 400 according to some
embodiments of the invention. The CD-ROM 400 may have stored
thereon a computer program comprising program instructions. The
computer program may be loadable (as shown by arrow 410) into an
electronic device 420 comprising a processing unit 440 and possibly
a separate memory unit 430. When loaded into the electronic device
420, the computer program may be stored in the memory unit 430.
According to some embodiments, the computer program may, when
loaded into the electronic device 420 and run by the processing
unit 440, cause the electronic device 420 to execute method steps
according to, for example, any of the methods shown in any of the
FIGS. 2 and 3. The electronic device 420 may, for example be a
communication device or a component of a communication device,
wherein the communication device is a network node, a base station,
a NodeB, a eNodeB, an access point, a home base station, a home
NodeB, a home eNodeB, a radio network controller, or a base station
controller.
[0107] FIG. 5 illustrates an example arrangement 500 according to
some embodiments of the invention.
[0108] The arrangement 500 comprises a load indicator 540 adapted
to keep track of a number of terminals that should be used in a
determination of whether to change mode or not. The load indicator
540 is arranged to receive signals from a receiver 530, which in
turn is connected to one or more antennas 510.
[0109] The arrangement 500 also comprises a comparator 550 adapted
to compare the number of terminals (furnished by the load indicator
540 to the comparator 550) to one or more thresholds (compare with
steps 221 and 261 of FIG. 2).
[0110] The comparator 550 is adapted to supply the results of the
comparisons to a mode determiner 560 of the arrangement 500, which
is adapted to determine whether or not the network node associated
with the arrangement should change mode (compare with steps 220 and
260 of FIG. 2).
[0111] The mode determiner 560 is adapted to inform a transmitter
520 (which is connected to the one or more antennas 510) and a
controller 570 of a determination that a mode change is to be
conducted.
[0112] The transmitter 520 is adapted to transmit an indication of
the mode change (compare with steps 230, 231 and 280 of FIG. 2) and
the controller 570 is arranged to change the operations of the
network node (e.g. of blocks 580 and 520) in accordance with the
new operation mode.
[0113] In some embodiments, functional blocks that already exist in
the further processing block 580 may be re-used in the arrangement
500. This may, for example, apply to the controller 570 and/or the
load indicator 540.
[0114] The described embodiments of the invention and their
equivalents may be realised in software or hardware or a
combination thereof. They may be performed by general-purpose
circuits associated with or integral to a communication device,
such as digital signal processors (DSP), central processing units
(CPU), co-processor units, field-programmable gate arrays (FPGA) or
other programmable hardware, or by specialized circuits such as for
example application-specific integrated circuits (ASIC). All such
forms are contemplated to be within the scope of the invention.
[0115] The invention may be embodied within an electronic apparatus
comprising circuitry/logic or performing methods according to any
of the embodiments of the invention. The electronic apparatus may,
for example, be a network node, a base station or a base station
controller.
[0116] According to some embodiments of the invention, a computer
program product comprises a computer readable medium such as, for
example, a diskette, a USB-stick or a CD-ROM (compare with FIG. 4).
The computer readable medium may have stored thereon a computer
program comprising program instructions. The computer program may
be loadable into a data-processing unit, which may, for example, be
comprised in a mobile terminal. When loaded into the
data-processing unit, the computer program may be stored in a
memory associated with or integral to the data-processing unit.
According to some embodiments, the computer program may, when
loaded into and run by the data-processing unit, cause the
data-processing unit to execute method steps according to, for
example, the methods shown in any of the FIGS. 2 and 3.
[0117] The invention has been described herein with reference to
various embodiments. However, a person skilled in the art would
recognize numerous variations to the described embodiments that
would still fall within the scope of the invention. For example,
the method embodiments described herein describes example methods
through method steps being performed in a certain order. However,
it is recognized that these sequences of events may take place in
another order without departing from the scope of the invention.
Furthermore, some method steps may be performed in parallel even
though they have been described as being performed in sequence.
[0118] In the same manner, it should be noted that in the
description of embodiments of the invention, the partition of
functional blocks into particular units is by no means limiting to
the invention. Contrarily, these partitions are merely examples.
Functional blocks described herein as one unit may be split into
two or more units. In the same manner, functional blocks that are
described herein as being implemented as two or more units may be
implemented as a single unit without departing from the scope of
the invention.
[0119] Hence, it should be understood that the limitations of the
described embodiments are merely for illustrative purpose and by no
means limiting. Instead, the scope of the invention is defined by
the appended claims rather than by the description, and all
variations that fall within the range of the claims are intended to
be embraced therein.
* * * * *